1. Field of the Invention
This invention relates to a technology for printing images on a print medium using a bi-directional reciprocating movement in a main scanning direction. The invention particularly relates to a technology for correcting printing positional deviation between forward and reverse passes.
2. Description of the Related Art
In recent years color printers that emit colored inks from a print head are coming into widespread use as computer output devices. In recent years, such color printers have been devised as multilevel printers able to print each pixel using a plurality of dots having different sizes. Such printers use relatively small ink droplets to form relatively small dots on a pixel position, and relatively large ink droplets to form relatively large dots on a pixel position. These printers can also print bi-directionally to increase the printing speed.
A problem that readily arises in bi-directional printing is that of deviation in printing position between forward and reverse printing passes in the main scanning direction caused by backlash in the main scanning drive mechanism and warping of the platen that supports the print media. JP-A-5-69625 is an example of a technology disclosed by the present applicants for solving this problem of positional deviation. This comprises of registering beforehand the printing deviation amount in the main scanning direction and using this printing deviation amount as a basis for correcting the positions at which dots are printed during forward and reverse passes.
However, in the case of bi-directional printing using multilevel printers, little consideration has been given to positional deviation arising between forward and reverse printing passes. Other problems include that while deviation may be corrected with respect to a particular one of the multiple colored inks, there is no correction of deviation in other ink colors. As a result, the deviation correction provides little improvement in the quality of the color image. The effect that positional deviation has on image quality is particularly large in halftone regions.